The code to generate multi-pack index learned to show (or not to
show) progress indicators.
* wb/midx-progress:
multi-pack-index: add [--[no-]progress] option.
midx: honor the MIDX_PROGRESS flag in midx_repack
midx: honor the MIDX_PROGRESS flag in verify_midx_file
midx: add progress to expire_midx_packs
midx: add progress to write_midx_file
midx: add MIDX_PROGRESS flag